A slider - Unlinked <---> 100% linked - allows from entirely independent gain reduction per channel all the way to fully linked (the current implementation).

For example the link control on the API 2500...

Right now the compressors in Reaper are locked into operating in stereo linked mode where every channel undergoes the same gain reduction. This can help with keeping a stable stereo image, but unlinked operation can lead to more transparent gain reduction and a more open feel, especially in a mastering context.

if you want to have 2 different compression setting on LEFT ADN RIGHT, just put 2 reacomp in you chain, on the first ont, you uncheck channel 2 (so you compress only left channel) and on the second, you uncheck channel 1